The present invention relates generally to air filter systems for small internal combustion engines, and more particularly to an air filter system for filtering debris from the cooling air entering the engine through the recoil starter housing.
In any air-cooled internal combustion engine, it is imperative that a continuous stream of cooling air be effectively directed over the hot cylinder block and crankcase surfaces during engine operation. In order to set up a cooling stream, a fan or blower is mounted on the flywheel end of the crankshaft. The fan can be a series of vanes on the surface of the flywheel, which are cast integrally with the wheel. If the vanes are on the outer surface of the flywheel, they are shaped in such a way that they draw air into the engine shroud, rather than push it through. Other designs use a stamped or pressed fan between the flywheel and the starter. Recently, recoil starters have been introduced that provide a flow of engine cooling air through the face of the starter housing and through the recoil pulley. Generally, the air entering the starter housing must be filtered, particularly in the case of lawn mowers, in which grass clippings can enter the cooling air stream and cause clogging between the shroud and the engine. Starter housings having perforated grilles may be successful in removing large particles from the cooling air stream; however, they are generally insufficient to remove smaller grass clippings as well as matted debris and dirt which may collect on the surfaces of the engine, or between the cooling fins. As a result of such accumulation, less surface area of the engine is exposed to the cooling air stream. In addition, the debris tends to insulate the hot metal surfaces from the cooling air stream. Therefore, it is desired to provide an air filter system that further inhibits the accumulation of dirt and debris from the cooling surfaces.